For instance, as disclosed in JP-A-2002-147485, torque fluctuation in a torque transmission system is conventionally absorbed by using a damper that is formed of elastic material such as rubber when a torque is transmitted from a driving-side rotating unit to a driven-side rotating unit. Here, in the damper disclosed in JP-A-2002-147485, an elastic coefficient k1 in a portion on which a torque acts in a normal rotation direction is greater than an elastic coefficient k2 in a portion on which a torque acts in a reverse rotation direction. The damper is thereby prevented from exceeding an elastic limit, so that the damper transmits a great torque along with absorbing the torque fluctuation.
A so-called direct injection type of an internal combustion engine, which directly supplies a combustion room with fuel, has greater torque fluctuation, due to its large fluctuation of a rotation angle, than a previously mixing type of an internal combustion engine that previously mixes fuel and air. Therefore, in the direct injection type of the internal combustion engine, the torque transmission system disclosed in JP-A-2002-147485 may not sufficiently absorb the torque fluctuation.
When the torque fluctuation is not sufficiently absorbed, various kinds of defects take place. Namely, a torque limiter wrongly acts, a fastening part between a shaft of a compressor and a hub of the torque transmission system loosens, or abnormal noise or aversive vibration takes place.